Near-ultraviolet excited broadband orange-yellow emitting Sr8MgIn(PO4)7:Eu2+ phosphors for WLEDs with high color rendering index

Abstract

As is well known, whitlockite β-Ca3(PO4)2-type phosphors are easily evolved to a new crystal structure by cation substitution, and have various crystallographic sites for doping activators to achieve luminescence. Herein, a novel broadband emitting Sr8MgIn(PO4)7: Eu2+ (SMIP) phosphor was prepared by high temperature solid state reaction. Its crystal structure was analyzed and refined via the Rietveld refinement method. The SMIP crystal presents a monoclinic system with space group C2/m. Their diffuse reflection and excitation spectra both show an intense absorption to the wavelength of 250–500 nm. And the photoluminescence spectrum exhibits a strong broadband emitting from 450 to 800 nm. Moreover, the luminescence decay curves reveal three kinds of Sr/Mg2+ crystallographic sites for Eu2+ occupying in SMIP host. For SMIP: xEu2+ samples, the optimized doping concentration was determined to be 0.03, and the energy transfer among the nearest-neighbor was dominating. Further, the activation energy was estimated to be 0.1145 eV. Finally, white light-emitting diodes (WLED) lamps were fabricated by coating the mixtures of SMIP: 0.03Eu2+ phosphors and BaMgAl10O17: Eu2+ phosphors on the surface of 400 nm near-ultraviolet chip. The optimized WLED lamp exhibits a correlated color temperature of 3034 K and a good color rendering index of 91.7. These results demonstrate the commercialized prospect of SMIP: Eu2+ materials as a broadband orange phosphor for application of solid state lighting.